1. Field of the Invention
The present invention relates to a welding transformer control apparatus provided with a thyristor in a resistance welding machine.
2. Prior Art
The conventional welding transformer control apparatus of this type operates to measure a current supplied to a primary winding or a secondary winding of a welding transformer and effect striking control, i.e., phase control by a thyristor at the primary winding of the welding transformer whereby the current supplied to the secondary winding of the welding transformer is controlled.
Since power voltage is generarlly varied greatly, the core of the transformer is sized so as not to generate magnetic saturation when the maximum voltage is supplied thereto. Hence, the power voltage has not been taken into consideration to control the prior art welding transformer.
There is a problem in that the transformer is large sized and heavyweight if the welding transformer is designed not to generate magnetic saturation when the maximum voltage is supplied to the welding transformer.
The present invention has been made in view of the problem set forth above and to provide a welding transformer control apparatus which permits the sue of a small sized and lightweight transformer, and is capable of preventing voltage greater than a predetermined voltage from being supplied to the welding transformer.
The welding transformer control apparatus comprises a voltage detecting circuit connected to a thyristor for detecting power voltage and a digital operation unit connected to the voltage detecting circuit via an A/D converter for receiving the digitized power voltage. The digital operation unit is also connected to a voltage setting unit for receiving a predetermined voltage to be supplied to the primary winding of the welding transformer. The digital operation unit compares the predetermined voltage supplied from the voltage setting unit with the power voltage supplied from the A/D converter and provides a signal to suppress the power voltage under the predetermined voltage. There is also provided a thyristor gate pulse generator connected between the digital operation unit and the thyristor for receiving the signal from the digital operation unit and providing a thyristor gate pulse to the thyristor so that the thyristor can effect striking control, i.e., phase control of the power supplied in the primary winding of the welding transformer whereby the voltage supplied to the primary winding of the welding transformer can be controlled under the desired voltage.
The above and other objects, features and advantages of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings.